The present invention relates to solvent resistant silicone compositions and more particularly relates to polysiloxane compositions having perfluoroalkylalkylene substituent groups which in the cured form produces an elastomer with exceptionally good resistance to hydrocarbon solvents, as well as good strength properties.
Silicone elastomers are widely valued for their resistance to moisture as well as high and low temperature stability characteristics. In certain cases where such properties are desirable, it is also desirable that the silicone elastomer have solvent resistance to hydrocarbon fluids and specifically such hydrocarbon fluids such as, gasoline, jet fuel and crude oil and various by-products of crude oil.
In a successful attempt to obtain a silicone elastomer with the high and low temperature stability of silicone elastomers and also good solvent resistance, fluorinated substituted polysiloxane compositions were developed. See, for instance, U.S. Pat. Nos. 2,979,519 of Pierce et al and 3,179,619 of Brown. The above patents recite methods and processes for producing heat cured silicone rubber compositions which cure to an elastomer having therein perfluoroalkylalkylene substituent groups which results in the final heat cured silicone elastomer having desirable solvent resistance to hydrocarbon fluids.
However, one of the disadvantages of such heat cured silicone rubber compositions is their high viscosities in the uncured state which may be as high as 50,000,000 centipoise at 25.degree. C. This is well known in heat cured silicone rubber technology and results in time consuming and expensive procedures in processing the heat cured silicone rubber composition in the uncured state. Accordingly, it is highly desirable to have a low viscosity composition in the uncured state which can be easily and economically processed to produce a solvent resistant fluorinated substituted silicone elastomer. Some attempts have been made to produce silicone compositions which in the uncured state have desirably low viscosities and also good physical properties comparable to that of the solvent resistant elastomers produced from heat vulcanizable silicone rubber compositions.
However, such attempts to produce such a silicone rubber composition, for instance, by incorporating fluorinated substituent groups in standard one-part room temperature vulcanizable silicone rubber compositions and a two-part room temperature vulcanizable silicone rubber composition have not been altogether successful.
The difficulty with one-part room temperature vulcanizable silicone rubber technology is that the composition has to be maintained in an anhydrous state prior to cure. Thus, such compositions are difficult to use in processing equipment for the purpose of fabricating desirable solvent resistant parts.
Accordingly, it was an unexpected discovery that SiH-olefin platinum catalyzed silicone rubber compositions could be produced which had desirable solvent resistant properties as well as physical properties comparable with that of the solvent resistant heat cured silicone rubber compositions.
It is one object of the present invention to produce a silicone rubber composition which can be cured at room temperature or elevated temperatures which is solvent resistant.
It is another object of the present invention to produce a silicone rubber composition which can be cured at room temperature or elevated temperatures which has physical properties comparable to that of heat vulcanizable silicone rubber compositions and which is solvent resistant.
It is an additional object of the present invention to produce silicone rubber compositions in which the polymers in the composition have fluorinated substituent groups and in which the curing mechanism comprises the reaction of a vinyl-containing polysiloxane with hydrogen containing silanes or polysiloxanes in the presence of a platinum catalyst.
It is yet an additional object of the present invention to provide for a process for economically and efficiently producing solvent resistant silicone rubber compositions.
It is still another object of the present invention to provide for a process for producing solvent resistant silicone rubber compositions which in the uncured state are of low viscosity and have excellent processability properties.
These and other objects of the present invention are explained by means of the disclosure below.